112 ORGANIC REMAINS. 
identity of time is afforded by the correspond- 
ence of the organic remains : in fact without 
these, the proofs of the lapse of such long periods 
as Geology shows to have been occupied in the 
formation of the strata of the Earth, would have 
been comparatively few and indecisive. 
The secrets of Nature, that are revealed to us, 
by the history of fossil Organic remains, form 
perhaps the most striking results at which we 
arrive from the study of Geology. It must 
appear almost incredible to those who have not 
minutely attended to natural phenomena, that 
the microscopic examination of a mass of rude 
and lifeless limestone should often disclose the 
curious fact, that large proportions of its sub- 
stance have once formed parts of living bodies. 
It is surprising to consider that the walls of our 
houses are sometimes composed of little else 
than comminuted shells, that were once the 
domicile of other animals, at the bottom of 
ancient seas and lakes. 
It is marvellous that mankind should have 
gone on for so many centuries in ignorance of 
the fact, which is now so fully demonstrated, 
that no small part of the present surface of 
the earth is derived from the remains of ani- 
mals, that constituted the population of ancient 
seas. Many extensive plains and massive 
mountains form, as it were, the great charnel- 
houses of preceding generations, in which the 
petrified exuviae of extinct races of animals and 
